Background: Our body responds by heat production and conservation when exposed to prolonged cold environment.Efficient thermogenesis is achieved by thyroid hormones.They are associated with the oxidative status of the body due to their role in metabolism. Ascorbic acid protects body from oxidative damage and neutralizes free radicals. Objective: To determine the effect of ascorbic acid supplementation on long term cold exposure induced changes in thyroid activity in Sprague-Dawley rats. Methodology: Nine weeks old healthy, male Sprague-Dawley rats, weighing 200±25 grams were included in this study. The study was approved by the ethical committee of RARE Rwp. Sample Size: Ninety healthy Sprague-Dawley rats (N=90) were randomly divided into three groups with thirty rats in each group. Control group (n = 30) These rats were fed on standard diet and kept at room temperature at 22±3°C. Cold Exposed Group (n = 30) Rats of this group were fed on standard diet. They were exposed to cold environment between 8-14°C for 1h/day for one month by keeping the cages in ice-filled tubs and recording the temperature by thermometer. Cold exposed with ascorbic acid supplementation group (n = 30) Rats of this group were fed on standard diet. They were given ascorbic acid (Vitamin C Ascorbic acid MERCK, research grade Cat No. 500074) supplement in a dose of 500mg/L mixed in drinking water. They were exposed to cold environment between 8-14°C for 1h/day for one month by keeping the cages in ice-filled tubs and recording the temperature by thermometer. Data collection: After one month of study, the rats were sacrificed and intracardiac blood sampling was done. The blood samples were analyzed for serum total tri-iodothyronine (T3), thyroxin (T4) and thyroid stimulating hormone (TSH) by using chemiluminescent immunometric assay on Siemens immulite 2000 analyzer. Results: Serum T3 levels were significantly different in control group, cold exposed group (47.35 ± 2.21 vs. 51.72 ± 6.81 vs. 50.92 ± 5.73, p-value =0.004) and cold exposed with ascorbic acid supplementation group. Serum T4 levels were also significantly (p-value = 0.002) different in control group (1.92 ± 0.47), cold exposed group (2.41 ± 0.58), and cold exposed with ascorbic acid supplementation group (2.09 ± 0.52). Serum TSH levels were also found highly significant (p-value = 0.000) in (0.16 ± 0.03) control group, cold exposed group (0.38 ± 0.13) and (0.29 ± 0.04) in the cold exposed with ascorbic acid supplementation group. Conclusion: Ascorbic acid prevents the cold induced changes in thyroid hormone levels.